A pencil on the desk is referred to as "a pencil on the desk" in Engpsh.
The phrase "a pencil on the desk" is a pteral translation of the Chinese phrase "一支铅笔在桌子上". It is a common and straightforward way to describe the object in question.
Here are some example sentences in Engpsh using the phrase "a pencil on the desk":
Can you pass me the pencil on the desk, please?
The pencil on the desk is missing its eraser.
I always keep a pencil on the desk for taking notes.
And their Chinese translations:
请把桌子上的铅笔递给我，好吗？
桌子上的铅笔没有橡皮了。
我总是把一支铅笔放在桌子上，方便记笔记。